- There is a body of evidence that suggests that the spontaneous pain and hyperalgesia associated with CMI is due to a dysregulation of intrinsic analgesic systems. The most well known intrinsic analgesic system is the endogenous opioid system, which appears to function normally in CMI. Another system, termed DNIC (Diffuse Noxious Inhibitory Controls), is characterized by widespread analgesia evoked by a noxious stimulus applied to anywhere on the body, such as tourniquet ischemia, or immersion of in painfully hot or cold water. The widespread nature of the DNIC effect, involving convergent second order neurons and a spinal-brain loop, is consistent with the diffuse widespread pain of CMI disorders such as FM. The results of several studies suggest that DNIC may be altered in CMI. Lautenbacher and Rollman observed that DNIC evoked by hot water immersion decreased the sensitivity to painful electrical stimuli in healthy control subjects but had no effect in patients with FM. Marchand [unpublished observations] has reported a similar effect using immersion of an arm in painfully hot water as both the conditioning and pain stimulus. This method shows an effect of DNIC on pain ratings in healthy controls but no effect in FM. Kosek and Hansson found that the DNIC manipulation of tourniquet ischemia decreased the sensitivity to painful pressure in control subjects but not in patients with FM.